The Shortcomings of Network Monitoring in Fighting ICS Threats

The growing sophistication of industrial control
system (ICS) networks, especially since the advent of the
Industrial Internet of Things (IIoT), has improved numerous
processes while also making them softer targets for attacks.
Simply put, interconnectedness has broadened and weakened the
attack surface.

In the past, attacks primarily originated from
rogue individuals, hacktivists, and disgruntled employees. But
in recent years, attacks have increasingly been orchestrated by
highly motivated and well-funded organizations, criminal gangs,
and countries bent on large-scale extortion and sabotage. One
carefully executed attack can accomplish as much, if not more,
than physical warfare.

Up until quite recently the IT infrastructure was
the command center for ensuring complete visibility, security
and control for threats — simply because the IT network was
always the focus of attacks. Meanwhile, ICS networks were
traditionally segregated and isolated. IIoT put an end to all
that.

To address new security threats, organizations need
better visibility, security, and control for their ICS
environments. Traditional passive monitoring alone, which has
its merits, simply cannot provide the level of detail required
to protect operational technology (OT) networks.

Device-level Threats may not cross the
network

In ICS environments, potentially dangerous behavior
and activity can occur on devices as well as the network.
However, many operations performed on a device will never
traverse the network. For example, asset inventory information
such as records of user log-ins and controller firmware
versions, as well as changes made to devices via direct
connections, rarely appear in network traffic. In addition,
some devices are rarely, if ever designed to talk on the
network. They are typically known as, “dormant
devices”.

As a result, passive network monitoring would not
detect a local attack on a device, where it can remain for
days, weeks, or even months without being
discovered.

Active monitoring queries all devices and
automatically gathers timely and comprehensive information
about them and their data. It will reveal details such as the
identity of the logged-in user, the firmware version in use,
and the open port list of a PLC/DCS controllers.

In addition, active monitoring can discover ‘blind
spots’ — such as dormant industrial devices that are connected
to a network but are not communicating. These blind spots are
never detected by passive monitoring.

Proactive Security

In addition, passive network monitoring can not
detect changes made to controller code, firmware, or
configuration of a device, whether the changes are authorized
or not.

Because of this weakness, a malicious actor who has
physical access to the network via a serial cable or USB can
make changes that will not be detected by network monitoring.
The same applies to threats from employees or contractors who
unknowingly expose controllers to attacks by using a device
infected with malware.

Both of the above scenarios can be addressed by
active monitoring, which periodically captures device snapshots
and compares them to known good baselines. It automatically
identifies and alerts on changes, in order to validate the
integrity of the device has not been compromised.

More importantly, active monitoring provides
complete awareness of current vulnerabilities that may put
industrial controllers at risk. This can prove invaluable when
new patches are issued. It allows the administrator to quickly
identify the devices that need to be patched and eliminates the
possibility of any specific device to be overlooked just
because it was not catalogued on a static inventory
spreadsheet.

Active monitoring of devices also gives meaning to
alerts since it provides contextual information such as who
logged into which device at a specific time, and what was the
impact of a specific change to a PLC. When a suspicious event
is detected, active monitoring can immediately query related
devices to assess whether they have also been affected. This
speeds up forensic analysis, mitigation, and the process of
returning devices to a known ‘good’ state.

Passive network security monitoring has its value
for identifying certain indicators of compromise (IoC), but
does not detect and mitigate all attacks or incidents on ICS
networks. To achieve in-depth visibility, security, and control
in OT environments, a hybrid active and passive approach is
needed.

Barak Perelman is CEO of , an
industrial cyber-security firm that improves operational
safety and reliability for industrial control networks by
providing situational awareness and real-time security.

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